This invention relates to packet-switched data communication networks, and particularly an Ethernet network or similar network wherein data may be transferred between two network stations, such as a hub or switch and another network station (particularly an end station such as a personal computer), at least two different rates, the hub and the other network station being able to establish a selected data rate by means of auto-negotiation. The invention is particularly though not necessarily exclusively intended for use with an auto-negotiation scheme as defined in IEEE 802.3u.
As switching and other technology has improved, the rate at which data may be transferred between network devices has increased. Currently there are various standards to which successive generations of network devices have been designed to operate. In particular, a standard data rate of 10 megabits per second has been partly planted by a standard of 100 megabits per second and is expected to be supplanted by an even faster rate, 1000 megabits per second. However, network devices operating according to obsolescent standards (i.e. the lower data rate) continued to be used. It therefore follows that it is known for a network switch or hub to be capable of exchanging data with another network station at a plurality of different selectable rates. It is also known, and specified in for example in the above mentioned network standard, for a hub and a station to which it is connected to commence a xe2x80x98conversationxe2x80x99 by a process of xe2x80x98auto-negotiationxe2x80x99, wherein a network hub or switch establishes by means of interrogation and response whether the other station is capable of transmitting and receiving data at the higher of two rates (or a rate which is practically the highest of a multiplicity of rates) so that thereafter the two stations exchange information or transmit information from one to the other at the selected higher or highest rate.
It is also known to maintain a connection between a hub and another station by means of a continuous sequence of symbols representing an xe2x80x98idlexe2x80x99 state. When one station at either end of the connection wishes to send data then by convention it sends at least a first symbol followed by a second symbol, representing a xe2x80x98carrierxe2x80x99 signal. The data then follows in the format defined by the appropriate standard. At the end of the data packet a third predetermined symbol followed by a fourth predetermined symbol is sent, so as to represent the end of the carrier. Such a sequence is conventionally repeated for each and every packet transmitted between the stations.
The present invention particularly relates to systems of this character and is concerned with a process for use with an auto-negotiation process, to monitor the quality of the connection, particularly a cable connecting a port on a network station to an end station.
If a multi-speed connection is used with badly installed cable or a cable or other link which does not meet an appropriate performance specification, then the reliability and throughput of the connection will be much reduced. The object of the present invention is to detect, by the monitoring of specific errors, the quality of the connection and, should the error rate representing a parameter of the quality of the cable exceed some selectable threshold, to cause the reduction of the data rate for the connection to a lower rate.
The present invention is based on the detection of the corruption of isolated idle symbols into a first symbol which would normally indicate the start of a data packet but is identifiable as an error when followed by an idle symbol. This specific form of error, known as false carrier and by convention written xe2x80x98FalseCarrierxe2x80x99, may be used as a reliable parameter of the quality of a connection between a hub and an end station in accordance with the invention.
In a preferred form of the invention, the method may be implemented on a 10/100 megabit per second hub repeater that uses auto-negotiation, as defined in IEEE 802.3u, to determine the data rate for a connection between the hub repeater and an end station. The 100 megabit per second connection transmits a sequence of xe2x80x98idlexe2x80x99 symbols to establish and maintain the link between the repeater and the end station. If these symbols are corrupted and the error rate of the false carriers increases above a certain threshold then the link may be downgraded to a data rate of 10 megabit per second.